His comments came as he was questioned about 22-year-old Aboriginal woman Ms Dhu, who died in August 2014 during her third hospital visit in three days after being locked up at South Hedland Police Station for failing to pay fines.

He said people in custody should be transported to hospital by ambulance like everyone else.

"If someone is sick, unconscious or unwell, they should never be transported from a police watch house in the back of a police van."

Mr O'Callaghan also told the inquiry he would like the police commissioner to have power to demote an officer without holding an internal hearing.

"It's a very complex, long process, sometimes it takes two or three years," he said.

"Then of course ... the moment's gone and it's not relevant anymore."

Mr O'Callaghan was giving evidence at the inquiry about the Corruption and Crime Commission, and said since former Supreme Court judge John McKechnie took over the watchdog in April 2015 he felt "comfortable".

He said he previously took issue with the CCC serving a section 42 notice, which prevented police internal investigators from doing their job, but that has not happened in two years.